Energy conservation techniques for industrial processes are frequently applied to process flue gas or other hot gaseous streams. Expander turbines may be employed in numerous continuous thermal processes to recover energy from the waste streams prior to venting. In petroleum refineries there are large scale combustion units, such as catalyst regeneration facilities, which produce flue gases in significant amounts. For instance, in modern petrochemical processes the oxidation of coke deposits on cracking catalysts or other hydrocarbon conversion media is carried out continuously or batchwise. A typical FCC unit transports fine catalyst particles from a cracking zone to a regeneration zone where air is passed over the coked catalyst at elevated temperature and pressure to produce a flue gas containing carbon oxides and other oxidation products. The flue gas from the regeneration stage contains entrained fine catalyst particles which are removed by conventional cyclonic separators, usually in 2-3 stages.
Due to the very high temperatures involved, materials of construction for the flue gas handling equipment often include refractory-lined carbon steel vessels and conduits. Although refractory linings are economically desirable for construction of high temperature apparatus, there is a possibility that spalling or attrition can cause hard solid particles to be broken off from the lining and propelled through the system into the flue gas, often travelling at speeds exceeding 30 meters/sec. The downstream turbine equipment employed in the power recovery train is easily damaged by solid particles and must be protected against the possibility of particles exceeding 1-5 mm. It is an object of the present invention to provide an improved device for retaining refractory particles or the like in power recovery trains to prevent turbine damage.